The relationship between socioeconomic status (SES) and health is well established for many health outcomes and in many contexts. Despite the research attention being paid to health inequalities, the physical mechanisms linking SES and health are poorly understood. Lifelong exposure to infections and inflammation has been proposed as an important determinant of mortality. Little is known about the social patterning of multiple chronic infections or immune function in the U.S. population and how these factors may contribute to health disparities. Psychosocial stress has also been proposed as a potential pathway whereby lower SES can harm one's health. There is a large body of research describing a consistent link between psychosocial stress and susceptibility to infection, as well as reduced immune control over existing infections. However, the role that SES may play in immune function via its effects on psychosocial stress is unknown. This project will advance current research on the potential role of infection, immunity and stress in health disparities using several datasets with different strengths. Using data from the National Health and Nutrition Examination Survey (NHANES) III (including confidential mortality data), the Sacramento Area Latino Study of Aging (SALSA), the Chicago Community Adult Health Survey (CCAHS), and the Health and Retirement Survey (HRS), we will first assess whether measures of SES are associated with the burden of chronic infection and immune response in the U.S population. Next, we will examine whether infectious burden and immune response mediate the relationship between SES and health outcomes such as mortality in the U.S. Finally, we will assess whether any relationships between SES and immune function are mediated by markers of psychosocial and economic stressors. We believe this work will fill important gaps in understanding the role that stress and the immune system might play in the interplay of social and biological risks that evolve over the life course to create disparities in disease and mortality. The results from this study may identify novel interventions for biological risk factors, such as the need for targeted vaccination or early treatment of common chronic infections. PUBLIC HEALTH RELEVANCE: This study proposes to explore the contribution of stress and immune function to health disparities in the U.S. population. Using several population level surveys with both economic and biological data, we will test relationships between socioeconomic status (SES) and the burden of chronic infection, as well as immune response to infection. We will test whether these immune and infection markers are related to psychosocial and economic stressors and whether they mediate the relationship between SES and health outcomes including mortality.